Occupant restraint systems for motor vehicles typically include a lap belt retractor for winding a lap belt taut about the occupant lower torso and a shoulder belt retractor for winding a diagonally disposed shoulder belt taut about the occupant upper torso. Such retractors typically include a reel having the belt attached thereto and a spiral or clock spring which rotates the reel in the belt winding direction.
It is characteristic of the aforedescribed conventional seat belt retractor that when the belt is fully unwound and buckled in a restraining position about a seated occupant, the spring is fully wound up and provides its highest level of winding bias upon the reel. This relatively high winding bias on the seat belt can be annoying, particularly in the shoulder belt retractor since the occupant must lean forward against the tension of the belt in order to reach the vehicle controls.
Accordingly prior patents such as Knierieman's U.S. Pat. No. 3,984,063, issued Oct. 5, 1976, and others recognize that the use of a primary spring and auxiliary spring can be employed to provide two different levels of winding tension on the belt, with the lower winding effort being applied to the belt when the belt is disposed in its restraining position about the occupant.
Still other prior patents, such as Magyar's U.S. Pat. No. 4,023,746, issued May 17, 1977, have proposed shoulder belt retractors in which a pawl is engageable with ratchet teeth carried on the reel to lock the reel against belt winding rotation so that the shoulder belt may be held at a slackened length about the occupant to further enhance occupant comfort.